Generally, a dust collector repeats such actions as making a primary deposit of powder to be collected on the surface layer of a planar filter cloth which is sewn in tubular or envelope shape to form a powder layer which prevents the powder from intruding inward and collect the powder on the primary powder layer; and then removing the collected powder by pulsating main body of the filter cloth by reversing inside/outside pressures of the filter cloth or like. Therefore, performance of the dust collector is controlled by how properly a balance of collection and removal is maintained.
For this reason, these filter cloths are desired to show low pressure loss (hereinafter, referred to as low pressure loss), high collection efficiency, no clogging, and superior dust shaking-off performance, and until now, various types of filter cloths have been proposed. For example, it is described that a method where a fiber layer on the surface of filter cloth is made to a dense structure or a laminated structure of fine fibers on the surface of filter cloth (see Patent Documents 1 to 3 below), and a method where a film such as mainly PTFE resin or a porous film is arranged on the surface layer (surface) (see Patent Document 4 below) are highly effective for the above requirements. However, depending on properties of the powder to be target, since airflow resistance is increased because the adherent layer of the powder forms a too dense structure, or the like, it cannot be necessarily said to be superior in functions thereof.
In addition, in order to obtain high speed filtration and low pressure loss of a dust collecting equipment, a means to increase filtration area of a filter cloth has been also employed. For example, a method such as pleating has been known (see Patent Documents 5 and 6 below). However, since collected dust deposits significantly in a trough part of pleats, the filter cloth as a whole does not have a function as an effective filtration area, and it cannot be said that this method increase filtration area in a form which is durable for a continuous use in the bag filter use. In addition, the following Patent Document 7 describes that superior air permeability can be obtained by a concave-convex sheet made of a nonwoven fabric having a concave-convex shape, but application to bag filter use was not successful due to insufficient strength.